It is well known in the art that complexes of nickel with phosphorous-containing ligands are useful as catalysts in hydrocyanation reactions. Such nickel complexes using monodentate phosphites are known to catalyze hydrocyanation of butadiene to produce a mixture of pentenenitriles. These catalysts are also useful in the subsequent hydrocyanation of pentenenitriles to produce adiponitrile, an important intermediate in the production of nylon. It is further known that bidentate phoshite and phosphinite ligands can be used to form nickel-based catalysts to perform such hydrocyanation reactions.
U.S. Pat. No. 3,903,120 discloses a process for preparing zerovalent nickel complexes by reacting elemental nickel with a monodentate phosphorous ligand of the formula PZ3 where Z is an alkyl or alkoxy group, preferably an aryloxy group. The process uses finely divided elemental nickel and is preferably carried out in the presence of a nitrile solvent. The reaction is taught to be carried out in the presence of excess ligand.
U.S. Pat. No. 3,846,461 discloses a process for preparing zerovalent nickel complexes of triorganophosphites by reacting triorganophosphite compounds with nickel chloride in the presence of a finely divided reducing metal which is more electropositive than nickel, and in the presence of a promoter selected from the group consisting of NH3, NH4X, Zn(NH3)2X2, and mixtures of NH4X and ZnX2, where X is a halide. Reducing metals include Na, Li, Mg, Ca, Ba, Sr, Ti, V, Fe, Co, Cu, Zn, Cd, Al, Ga, In, Sn, Pb, and Th, with Zn being preferred.
U.S. Pat. No. 5,523,453 discloses a method of preparing nickel hydrocyanation catalysts containing bidentate phosphorous ligands. Zero-valent nickel compounds that contain ligands that can be displaced by the bidentate phosphorous ligand are a preferred source of nickel. Two such compounds are Ni(COD)2, where COD is 1,5-cyclooctadiene, and (oTTP)2Ni(C2H4), where OTTP is P(O-ortho-C6H4CH3)3. Alternatively, divalent nickel compounds may be combined with reducing agents to produce a suitable nickel source. In the latter method of preparing catalyst, as the temperature of the catalyst preparation increases, the catalyst formation rate increases, but the amount of degradation product also increases. Accordingly, there is a need in the art for a process that allows for high reaction rates and low degradation.